Vacuum electric tube device



Aug. 16, 1932. E. Y. ROBINSON 1,872,344

VACUUM ELECTRIC TUBE DEVICE Filed NOV. '7, 1927 3 II x f H x :l II II II I II i ii 2 Fig.3.

WITNESSES: INVENTOR Err) as? X Robinson ATTORN EY Patented Aug. 16, 1932 UNITED STATES PATENT OFFICE nnnnsr YEQMAN ROBINSON, on BUSHVILII'LL PARK, ENFIELD, ENGLAND, ASSIGNOR T0 nssoom'rnn ELECTRICAL INDUSTRIES LIMITED, A COMPANY or Qumranmam VACUUM fnnnomnrc TUBE v nnvrcn Application filedlNovember 7, 1927, Serial No. acreage, and me amen} November- 9', 1926." p

This invention relatesto vacuum electric tube devices of the kind: which have a plurality of electrodes includinga filamentary electrode such as an electron-emitting cathode which operates with'a potential drop along it such as by reason of a heating currentto render the filament, electron-emitting.

' In vacuum electric tube devices, a filamentary cathode is of necessity supported at its two ends in order that heating current may be led into it. In certain cases it is desirable to support a filament Cathode at additional points which are intermediate between its ends for various reasons of which the following may be mentioned. When filaments are tensioned by means of springs the vacuum electric tube device tends to be what, is called microphonic and springs may be eliminated by supporting the filament at points which are comparatively close together so thatcsagging is reduced! Such supportsmay be employed when the separations between the elec-, trodes are required to be small. By employ.- ing a filament of hairpin or zig-zag forma-, tion it is generally possible to make the valve more compact than is the case when the oathode comprises a single straight length of filament. Y I e i r Heretofore intermediate points of filament cathodes have been supported by means of metal hooks which are insulated from the ends of the filament and of course from other electrodes by reason of the fact that they are supported from an insulating member for instance, by being embedded in a glass bead or rod or framework. Such supports cause an undesirable cooling of the bight portions of th l ment. V fAccor-ding to the present invention filamentary members which operate with a potential drop or which depend for their operation on being at an elevated temperature are support d at o r m p i t i b tween their extremities by supporting, reg tering, nstraining or restrainingmembers which are inherently insulators and which embrace wholly or in part the filamentary me1nberS-,, Such filamentary mem bers may be made of hairpin or zig-zag formation and supported as above set forth at their bight portions. The members are preferably in the form of hooks or eyes and supportedor reinforced by metal. They preferably consist of metal members coated with insulating material. By the invention the intermediate portions of the filament are not appreciably cooled by the insulation hooks or members and the construction of vacuum electric tube devices may be simplified'by reason of the'fact that heat insulators are also good electricalinsulators and consequently in some cases the usual type of insulation is unnecessary.

In some cases a filament of hairpin formation may be freely supported so that the bight portion is not secured although its motion-is limited by an insulated hook or eye. I For example, if the hook is of metal vibration of the filament will cause a periodic cooling of the bight portion, whilst-the use of an insulated hook will eliminate or greatly reduce such cooling. In a similar manner a filament having an axial tension may be restrained by an insulating member at points intermediate between its extremities. f

To reduce the separation of electrodes and to reduce microphony it is desirable to sup port the filament at as many points intermediate between its extremities as feasible.

With metal hooks as hitherto employed filaments have'been supported or restrained at intermediate points as little as possible because such hooks cool the filament thus reducing the cathode eflic'iency and giving unequal heating. By the use of this invention the filament may be supported at a large number of points .or closely restrained with? out being subjected to these defects.

In the preferred form a hook or support consists of a shaped metal member, such as a wire bent to the form of a hook or eye and provided with an insulating coating at least on the part thereof over which the bight portion of the filament passes. Such support, at its uncoated portion, may be rigidly welded or otherwise attached to a metal structure so that when comparatively small differences of potential are in question further insulation than that provided by the coating is unnecessary. The insulating coating material is chosen to suit the operating temperature of the filament. For oxide coated platinum-iridium filaments the coating conveniently comprises kaolin, porcelain or other fictile material or quartz.

The insulating member may be formed separately, and be supported by a metal support or reinforcing member. -The metal support or reinforcing member may be attached to a supportingframework or to another electrode of the device that may serve as a'supporting framework, which latter construction can be employed when there will not be a large difierence of potential between such further electrode and the filament and when the extra capacity introduced is of little importance. For example such modification is particularly suitable where of the order of 0.1 or 0.2 mm.

the additional electrode operates at a fixed potential, as for example the so-called space charge grid in four electrode valves.

t has been found that a metal hook coated with kaolin, as hereafter described, will withstand a considerable potential difierence,

for example 40 volts, even when the insulation is at red heat andits thickness is only This invention is therefore not restricted to cases wherein the potential difference across the insulation is small, but is notably applicable in such cases.

To enable the invention to be clearly un derstood several insulated members and elec trode structures individually forming features of the invention will now be described with reference to the accompanying drawing in which Fig. 1 illustrates on an enlarged scale one form of insulated hook. Fig. 2 represents a form of electrode structure from which the anode is omitted for the sake of clearness, Fig. 3 showing the filament unit separated.

Referring to Fig. 1 this illustrates in section a filament. In providing the coating 3 according to a convenient method the hookshaped wire 1 is dipped into a kaolin or porcelain slip and then warmed to a red heat, in a flame for xample, to dry the adhering coating. Several such coatings are, if necessary, applied in this manner until the desired thickness of insulation is obtained. If the hook is to support or restrain an oxide coated. filament three such coatings will usually be sufficient. Finally, the hook'coated as just above described is fired to a high temperature to sinter or vitrify or fuse the porcelain. This heating is conveniently effected by holding the hook for a few seconds in a blow-pipe flame, care being taken that the molybdenum or tungsten crystals are not appropriate length, the hook and quartz cov-' ering being bentto the required shape in a blow-pipe flame.

teferring to Figs. 2 and 3 inclusive, the structure shown in Fig. 2 is of known kind so far as the anode and grid are concerned. The anode is omitted for the sake of clearness, whilst the grid '20is shown in position.

The cathode which is shown separately in Fig. 3 is of M-sha-pe and comprises two portions 25 and 26 connected electrically in parallel. These filaments are supported on a framework in the following manner. The framework is formed of a wire 27 of inverted U-shape, the free arms of which are adapted to bewelded to the supports 28. The two upper bight portions of the filament are carried upon insulated hooks 29 which may be of the kind shown in Fig. 1 welded to the frame wire 27. The free ends of the filament are attached to metal tabs 30 welded to the side arms of the wire 27, whilst the lower bight portion is'attached to a member 31 which is carried upon a cross wire 32. The filament is mounted on the framework before being assembled on the pres 15, the wire 31 being welded to a lead-in wire 33 and the wire 32 being thereafter cut through or removed. Current is carried to the filament through the lead-in wire 33 and through a lead-in wire connected to one of the supports 28. In the example shown the filament is not placed in tension, but springs may be incorporated if desired in the insulated hook members 29.

I claim as my invention V 1. The method of mounting a filament on the supporting wires of a press comprising the steps of forming two portions into a closed frame, connecting the ends of the filae ment to spaced points on said frame, attachjacent the ends of one side of said polygon and stretching said filament between insulated supports positioned at other points on the sides of said polygon, welding said frame adjacent the ends of said one side to said supporting wires of the press, and cutting out said one side of said polygon.

In testimony whereof I have hereunto subscribed my name this twenty-fifth day of October, 1927. i

ERNEST YEOMAN ROBINSON. 

